Fixing units which are equipped with a heating roller as a heating member and a pressing roller as a pressing member which is pressed against the heating roller are provided conventionally as units used in image forming apparatus such as laser printers. In fixing units of this kind, thermal fixing is performed in such a manner that a sheet (recording subject medium) to which a toner image has been transferred is held between and transported by the two rollers. Further, in fixing units of this kind, to enable smooth transport of a sheet that has been subjected to fixing, a peeling nail for peeling the sheet off the heating roller is disposed downstream of the holding position in the sheet transport direction of the fixing unit.
Incidentally, in the above-described conventional image forming apparatus, if the distance between the peeling nail and the holding position (what is called a nip position) where a sheet is held between the heating roller and the pressing roller is large, a problem arises that a sheet that has been subjected to fixing behaves differently depending on its state (i.e., its behavior tends to be unstable) as exemplified by the sheet's being peeled off immediately after passing the nip position without being peeled off by the peeling nail and the sheet's being transported to the position of the peeling nail and peeled off forcibly by it. If the sheet behavior is so unstable, trouble (e.g., sheet waving) due to deviation from an assumed sheet transport path tends to occur and nay prevent smooth and highly accurate image formation. To make such trouble less likely, it is desirable to dispose the peeling nail closer to the nip position so that a sheet is not peeled off at a position that is unduly away from the nip position (in other words, it is desirable to peel off a sheet stably near the nip position). However, an attempt to dispose the peeling nail closer to the nip position so that a sheet is peeled off stably near the nip position makes part of the peeling nail prone to interfere with a sheet being transported, resulting in a problem that it prevents good image formation.
The invention has been made in view of the above circumstances, and provides, in a device which performs thermal fixing by means of a heating member and a pressing member, a configuration capable of satisfactorily peeling off a recording medium that has been subjected to fixing while effectively preventing interference between a peeling member and a recording subject medium.